(a) Field of the Invention
The present invention relates to a sheet feeder having an intermittent coupling member and, more particularly, an improvement of a sheet feeder suitable for use in an imaging device such as a printer. The present invention also relates to a method for controlling such a sheet feeder and a cut-out gear suitable for use in the sheet feeder.
(b) Description of the Related Art
A conventional sheet feeder for use in a printer is described in Patent Publication No. JP-A-62(1987) -215437, for example. The described sheet feeder comprises a pickup roller and a gear train including a sun and planet gear receiving a driving force from a platen gear and a cut-out gear having a part of lacking teeth for effecting an idling state in the mechanical coupling. A specified amount of rotation in a forward rotation of the platen gear is transmitted to the pickup roller through the gear train after a reverse rotation of the platen.
FIG. 1 shows the conventional sheet feeder as mentioned above, wherein the sheet feeder comprises a first idle gear 141 engaged with a gear 148 fixed to a platen shaft 152, a second idle gear 142 constituting a planet gear linked with the shaft of the first idle gear 141, a third idle gear 143 engaged with the first idle gear 141, a fourth idle gear 144 co-axially fixed to the third idle gear 143, a fifth idle gear 145 engaged with the fourth idle gear 144, a pickup roller gear 146 engaged with the fifth idle gear 145 and co-axially fixed to a pickup roller 151 disposed for feeding a cut sheet 160 from a pile of cut sheets.
The third idle gear 143 and the fourth idle gear 144 have respective cut-out portions 153 or lacking teeth parts, which are opposed to each other. The lacking teeth part 153 of the third idle gear 143 disengages the third idle gear 143 with the fourth idle gear 144 after the engagement of the fourth idle gear 144 and the fifth idle gear 145 is finished due to the lacking teeth part of the fourth idle gear 144.
In operation, the gear train is subjected to a reverse rotation designated by arrow "b", after some forward rotation designated by arrow "a", to engage the gear train. The gear train allows the pickup roller 151 first to feed the cut sheet 160 in the reverse direction up to the position behind the platen shaft 152 and then to feed the cut sheet 160 in the forward direction, thereby feeding the cut sheet 160 from the sheet feeder.
In the above conventional sheet feeder, a skew of the cut sheet is not corrected unless the operator of the printer corrects after stopping the sheet feeder.